This study is designed to determine: 1) Incidence and relative risk of primary hepatocellular carcinoma (PHC) among hepatitis B virus (HBV) carriers compared to non-carriers, and 2) whether alpha-fetoprotein (AFP) can be used as a practical screening method for early PHC detection. The population cohort is 20,000 male Chinese government employees in Taiwan age 40-59 who have mandatory health and life insurance which assures medical care for illness and detection of disease. HBV carriers constitute 15 percent of this population and are at increased risk of developing PHC, the leading malignant neoplasm in Taiwan. HBV carriers and a matched cohort of non-carriers are tested yearly for HBV markers to determine changes in infection status and for AFP (radioimmunoassay) to detect preclinical PHC.